The present invention relates to a seat load measuring apparatus for measuring a seat load applied to a seat of a vehicle, such as an automobile, by the weight of an occupant sitting on the seat. Particularly, the present invention pertains to a seat load measuring apparatus which can be flexibly and effectively adopted to various kinds of motor vehicles.
A conventional automobile is equipped with seat belt devices and airbag devices. These devices are provided for restraining the inertial movement of occupants so as to protect the occupants in the event of an emergency such as a vehicle collision at which large deceleration is exerted on the vehicle.
The amount of the inertial force acting on the occupant depends on the weight of the occupant sitting on the vehicle seat. If the seat belt device and the airbag device are invariably controlled regardless of the weight of the occupant, it is difficult to make these devices effectively restrain the occupant in relation to the inertial force acting on the occupant. In recent years, there has been a proposal to control the actions of these safety devices based on the weight (body weight) of an occupant sitting in a vehicle seat in order to make the seat belt device and the airbag device restrain the occupant more effectively. For example, adjusting the amount of gas for deploying the airbag, the airbag inflating speed, and/or the magnitude of pretension of the seat belt depending on the weight of the occupant.
In order to control the actions of the seat belt device and the airbag device depending on the weight of the occupant sitting on the vehicle seat, it is necessary to measure the weight of the occupant. To achieve this, it has been proposed that a vehicle seat be provided with a seat load measuring apparatus for measuring the weight of an occupant sitting on the vehicle seat.
The seat load measuring apparatus requires load sensors for detecting the magnitude of load applied to the vehicle seat by the weight of the occupant. There are some seat load measuring apparatuses employing strain gauges as the load sensors (for example, see Japanese Unexamined Patent Publication No. H11-304579, Japanese Unexamined Patent Publication No. H11-351952, Japanese Patent Unexamined Publication No. 2001-304949) (both of which are incorporated by reference herein in their entireties).
Load sensors to be used for this purpose require a high degree of detection accuracy and adequate fracture strength. In general, the load sensor should have a detection accuracy that enables it to detect a load fluctuation of about 100 g in the gravitational direction. The accuracy must not be affected even when a load of 100 kg is applied in any direction other than the gravitational direction. In regards to the strength of the load sensor, it is required that the sensor effectively and securely withstand a large load in the event of a vehicle collision.
One problem frequently encountered is that in the event of a vehicle collision, large deceleration may act on a vehicle body so as to momentarily lift up the rear side of a vehicle seat where the seat load measuring apparatus is mounted.
For an apparatus with a strain gauge as a load sensor, the gauge, disposed on a sensor plate is deflected and deformed depending on the magnitude of load applied to the vehicle seat. The sensor plate is connected to a cable which connects to an electronic control unit (ECU) mounted on the vehicle so that a casing for the load sensor and the cable are united. However, different types of vehicles require the cable to be different lengths. Therefore, manufacturers must produce load sensors with varying cable lengths resulting in an increase in production costs.
Further, since the cable is attached to the load sensor, it is troublesome to mount the sensor plate to the body of the load sensor. As a result, such a seat load measuring apparatus is difficult to install, maintain and manufacture.